Apparatus and method for transmitting a sub-channel signal in a communication system using an orthogonal frequency division multiple access scheme

ABSTRACT

Methods of transmitting an receiving symbols by a Mobile Subscriber Station (MSS) and a Base Station (BS) are provided. The method for receiving symbols by the MSS includes receiving symbols from the BS, wherein the symbols are mapped onto data sub-carriers using a sequence, wherein the sequence includes result values, the result values being generated by applying, to a basic sequence, an offset and a number of cyclic shifting, the basic sequence having a length identical to the number of data sub-carriers. The method for transmitting symbols by the MSS includes transmitting symbols to the BS, wherein the symbols are mapped onto data sub-carriers using a sequence, wherein the sequence includes result values, the result values being generated by applying, to a basic sequence, an offset and a number of cyclic shifting, the basic sequence having a length identical to the number of data sub-carriers.

PRIORITY

This application is a continuation of application Ser. No. 12/049,706,filed on Mar. 17, 2008, which is a continuation of application Ser. No.11/077,858, filed Mar. 11, 2005, and claims priority under 35 U.S.C.§119 to an application entitled “Apparatus And Method For TransmittingSub-Channel Signal In Communication System Using Orthogonal FrequencyDivision Multiple Access Scheme” filed in the Korean IntellectualProperty Office on Mar. 12, 2004 and assigned Serial No. 2004-17065, andan application entitled “Apparatus And Method for TransmittingSub-Channel Signal In Communication System Using Orthogonal FrequencyDivision Multiple Access Scheme” filed in the Korean IntellectualProperty Office on Apr. 12, 2004 and assigned Serial No. 2004-25145, thecontents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a communication system usingan orthogonal frequency division multiple access (OFDMA) scheme. Moreparticularly, the present invention relates to an apparatus and a methodfor transmitting a sub-channel signal while minimizing interferencebetween adjacent cells.

2. Description of the Related Art

Recently, various studies and research have been performed for 4^(th)generation (4G) communication systems in order to provide subscriberswith services having superior quality of service (QoS) at a highertransmission rate. In particular, many studies are being performed withthe 4 G communication systems in order to provide subscribers with highspeed services by ensuring mobility and QoS to wireless local areanetwork (LAN) communication systems and wireless metropolitan areanetwork (MAN) communication systems, which can provide services at arelatively high rate.

In order to support a broadband transmission network for a physicalchannel of the wireless MAN communication system, an institute ofelectrical and electronics engineers (IEEE) 802.16a communication systemusing an orthogonal frequency division multiplexing (OFDM) scheme and anOFDMA scheme has been suggested. According to the IEEE 802.16acommunication system, the OFDM/OFDMA schemes are applied to the wirelessMAN system to transmit a physical channel signal using a plurality ofsub-carriers with a high transmission rate.

The IEEE 802.16a communication system is based on a single cellstructure without taking mobility of a subscriber station (SS) intoconsideration. Additionally, an IEEE 802.16e communication system, whichtakes mobility of the SS into consideration based on the IEEE 802.16acommunication system, has been suggested. The IEEE 802.16e communicationsystem considers the mobility of the SS under a multi-cell environment.In order to permit the mobility of the SS under the multi-cellenvironment, operational relationship between the SS and a base station(BS) must be changed. Accordingly, studies have been performed with ahandover of the SS in order to support the mobility of the SS under amulti-cell structure. Herein, the SS having the mobility is called amobile subscriber station (MSS).

FIG. 1 is a schematic view illustrating a conventional IEEE 802.16ecommunication system. Referring to FIG. 1, the conventional IEEE 802.16ecommunication system has a multi-cell structure including a cell 100 anda cell 150. The conventional IEEE 802.16e communication system includesa BS 110 for managing the cell 100, a BS 140 for managing the cell 150,and a plurality of MSSs 111, 113, 130, 151, and 153. The BSs 110 and 140communicate with the MSSs 111, 113, 130, 151, and 153 using theOFDM/OFDMA scheme.

The conventional IEEE 802.16e communication system performs an inversefast Fourier transform (IFFT). For example, the conventional IEEE802.16e communication system uses 1702 sub-carriers. Among the 1702sub-carriers, 166 sub-carriers are used as pilot sub-carriers and 1536sub-carriers are used as data sub-carriers. In addition, the 1536sub-carriers are divided into 32 sub-channels including 48 sub-carriers,respectively. The sub-channels are allocated to the MSSs according tothe state of the system. Herein, the sub-channel signifies a channelincluding at least one sub-carrier. For example, 48 sub-carriers mayform one sub-channel.

The sub-channel can be formed through two schemes in the conventionalIEEE 802.16e communication system.

According to the first scheme, the sub-carriers forming the sub-channelsare dispersed over all frequency bands of the sub-carriers. Inparticular, sub-carriers are dispersed over the entire frequency band ofthe data sub-carriers, thereby obtaining a frequency diversity gain.

According to the second scheme, the sub-carriers forming thesub-channels are aligned in the form of adjacent sub-carriers withoutbeing dispersed over all frequency bands of the sub-carriers.

If the sub-channels are formed according to the second scheme, adjacentcells may use the same sub-channel in the same unit time slot. Herein,the same sub-channel signifies the sub-channels including thesub-carriers having the same frequency band. That is, as described withreference to FIG. 1, two adjacent cells (cells 100 and 150) may use thesame sub-channel in the same unit time slot.

More specifically, if cells 100 and 150 select the same sub-channel andthe same modulation and coding scheme (MCS) is applied to the samesub-channel, the MSS 130, which is located in a cell boundary area, canreceive the signal from the BS 110, and also from the BS 140, if thesignal has high strength. For example, if the signal has a high carrierto interference and noise ratio (CINR), the MSS 130 receives the signaland demodulates the signal into information data.

If the conventional IEEE 802.16e communication system having a frequencyreuse factor of 1 forms the sub-channels according to the second scheme,the sub-channels of the cells forming the conventional IEEE 802.16ecommunication system have the same frequency band. If the same MCS isapplied to the sub-channels of the cells, the MSS located in the cellboundary area can receive the sub-channel signals not only from the BSof the MSS, but also from other BS. As a result, the MSS may receive thesub-channel signal having the higher interference component.Accordingly, it is necessary to provide an apparatus and a method fortransceiving the sub-channel signal, while minimizing interferencebetween adjacent cells.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve the aboveand other problems occurring in the prior art. An object of the presentinvention is to provide an apparatus and a method for transmitting asub-channel signal in an OFDMA communication system.

Another object of the present invention is to provide an apparatus and amethod for interleaving a sub-channel signal in such a manner thatsub-channels having adjacent sub-carriers can be differentiated fromeach other according to BSs thereof in an OFDMA communication system.

In order to accomplish the above and other objects, according to a firstaspect of the present invention, there is provided a method forreceiving symbols by a mobile subscriber station (MSS) in acommunication system. The method includes receiving symbols from a basestation (BS), wherein the symbols are mapped onto data sub-carriersusing a sequence, wherein the sequence includes result values, theresult values being generated by applying, to a basic sequence, anoffset and a number of cyclic shifting, the basic sequence having alength identical to the number of data sub-carriers,

wherein the sequence is expressed as:

${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$

where P_(f) ^(g)(j) is a j^(th) element of the sequence, P_(f)(j) is aj^(th) element of the cyclic shifted basic sequence, which is generatedby cyclic-shifting the basic sequence in a left direction by f times, fis an integer value selected from 0 to M−1, g is the offset having aninteger value from 0 to M, and M is the number of the data sub-carriers,and

wherein f and g are determined according to:

f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$

wherein, PERM is M which is the number of data sub-carriers, OFFSET isM+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.

According to another aspect of the present invention, there is provideda method for transmitting symbols by a mobile subscriber station (MSS)in a communication system. The method includes transmitting symbols to abase station (BS), wherein the symbols are mapped onto data sub-carriersusing a sequence, wherein the sequence includes result values, theresult values being generated by applying, to a basic sequence, anoffset and a number of cyclic shifting, the basic sequence having alength identical to the number of data sub-carriers,

wherein the sequence is expressed as:

${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$

where P_(f) ^(g)(j) is a element of the sequence, P_(f)(j) is a elementof the cyclic shifted basic sequence, which is generated bycyclic-shifting the basic sequence in a left direction by f times, f isan integer value selected from 0 to M−1, g is the offset having aninteger value from 0 to M, and M is the number of the data sub-carriers,and

wherein f and g are determined according to:

f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$

wherein, PERM is M which is the number of data sub-carriers, OFFSET isM+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.

According to another aspect of the present invention, there is provideda method for transmitting symbols by a base station (BS) in acommunication system. The method includes transmitting symbols to amobile subscriber station (MSS), wherein the symbols are mapped ontodata sub-carriers using a sequence, wherein the sequence includes resultvalues, the result values being generated by applying, to a basicsequence, an offset and a number of cyclic shifting, the basic sequencehaving a length identical to the number of data sub-carriers, whereinthe sequence is expressed as:

${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$

where P_(f) ^(g)(j) is a j^(th) element of the sequence, P_(f)(j) is aj^(th) element of the cyclic shifted basic sequence, which is generatedby cyclic-shifting the basic sequence in a left direction by f times, fis an integer value selected from 0 to M−1, g is the offset having aninteger value from 0 to M, and M is the number of the data sub-carriers,and

wherein f and g are determined according to:

f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$

wherein, PERM is M which is the number of data sub-carriers, OFFSET isM+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.

According to another aspect of the present invention, there is provideda method for receiving symbols by a base station (BS) in a communicationsystem. The method includes receiving symbols from a mobile subscriberstation (MSS), wherein the symbols are mapped onto data sub-carriersusing a sequence, wherein the sequence includes result values, theresult values being generated by applying, to a basic sequence, anoffset and a number of cyclic shifting, the basic sequence having alength identical to the number of data sub-carriers,

-   -   wherein the sequence is expressed as:

${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$

where P_(f) ^(g)(j) is a j^(th) element of the sequence, P_(f)(j) is aj^(th) element of the cyclic shifted basic sequence, which is generatedby cyclic-shifting the basic sequence in a left direction by f times, fis an integer value selected from 0 to M−1, g is the offset having aninteger value from 0 to M, and M is the number of the data sub-carriers,and

wherein f and g are determined according to:

f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$

wherein, PERM is M which is the number of data sub-carriers, OFFSET isM+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating a conventional IEEE 802.16ecommunication system;

FIG. 2 is a schematic view illustrating a transmitter for an IEEE802.16e communication system according to an embodiment of the presentinvention;

FIG. 3 is a schematic view illustrating an interleaving procedure for asub-channel signal in an IEEE 802.16e communication system according toan embodiment of the present invention; and

FIG. 4 is a flowchart illustrating a procedure for transmitting asub-channel signal in an IEEE 802.16e communication system according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will be described indetail herein below with reference to the accompanying drawings. In thefollowing detailed description, a detailed description of knownfunctions and configurations incorporated herein will be omitted when itmay obscure the subject matter of the present invention.

The present invention is directed to an orthogonal frequency divisionmultiple access (OFDMA) communication system. More specifically, thepresent invention suggests an interleaving scheme for a sub-channelsignal capable of minimizing interference between adjacent cells in aninstitute of electrical and electronics engineers (IEEE) 802.16ecommunication system. That is, the present invention suggests aninterleaving scheme for a sub-channel signal capable of minimizinginterference between adjacent cells when the IEEE 802.16e communicationsystem has a frequency reuse factor of 1, i.e., when cells forming theIEEE 802.16e communication system use the same frequency band.

It should also be noted that although the present invention will bedescribed in relation to the IEEE 802.16e communication system, theinterleaving scheme for the sub-channel according to the presentinvention is applicable for other systems using the OFDMA scheme.

FIG. 2 is a schematic view illustrating a transmitter for an IEEE802.16e communication system according to an embodiment of the presentinvention. Referring to FIG. 2, the transmitter includes a cyclicredundancy check (CRC) inserter 211, an encoder 213, a symbol mapper215, a sub-channel allocator 217, a serial to parallel converter 219, apilot symbol inserter 221, an inverse fast Fourier transform (IFFT) unit223, a parallel to serial converter 225, a guard interval inserter 227,a digital to analog converter 229, and a radio frequency (RF) processor231.

When user data bits and control data bits to be transmitted aregenerated, the user data bits and control data bits are input into theCRC inserter 211. Herein, the user data bits and control data bits arecalled “information data bits”. The CRC inserter 211 inserts a CRC bitinto the information data bits and outputs the information data bits tothe encoder 213.

Upon receiving the signal from the CRC inserter 211, the encoder 213codes the signal through a predetermined coding scheme and outputs thecoded signal to the symbol mapper 215. Herein, the predetermined codingscheme includes a turbo coding scheme having a predetermined coding rateor a convolutional coding scheme.

The symbol mapper 215 modulates the coded bits output from the encoder213 through a predetermined modulation scheme, thereby forming amodulation symbol. The modulation symbol is output to the sub-channelallocator 217. Herein, the predetermined modulation scheme includes aquadrature phase shift keying (QPSK) scheme or a 16 quadrature amplitudemodulation (QAM) scheme.

The sub-channel allocator 217 receives the modulation symbols from thesymbol mapper 215, allocates the modulation symbols to the sub-channels,and outputs the modulation symbols to the serial to parallel converter219. The sub-channel allocator 217 allocates the sub-channels to themodulation symbols through a predetermined scheme. That is, because theIEEE 802.16e communication system has a frequency reuse factor of 1, thesub-channel allocator 217 allocates the sub-channels to the modulationsymbols, after interleaving the sub-channel signal, such thatinterference between adjacent cells can be minimized. This allocationscheme will be described later in detail.

Upon receiving the serial modulation symbols having the sub-channelsfrom the sub-channel allocator 217, the serial to parallel converter 219parallel-converts the modulation symbols and outputs the modulationsymbols to the pilot symbol inserter 221. The pilot symbol inserter 221inserts pilot symbols into the parallel modulation symbols and outputsthe parallel modulation symbols to the IFFT unit 223. The IFFT unit 223receiving the signal output from the pilot symbol inserter 221 performsan N-point IFFT with respect to the signal and sends the signal to theparallel to serial converter 225.

Upon receiving the parallel signal from the IFFT unit 223, the parallelto serial converter 225 converts parallel signal into the serial signaland outputs the serial signal to the guard interval inserter 227. Afterreceiving the serial signal output from the parallel to serial converter225, the guard interval inserter 227 inserts a guard interval signalinto the serial signal and outputs the serial signal to the digital toanalog converter 229. Herein, the guard interval is used for removinginterference between orthogonal frequency division multiplexing (OFDM)symbols, which have been transmitted in previous OFDM symbol time, andOFDM symbols to be transmitted in present OFDM symbol time when an OFDMAcommunication system transmits the OFDM symbols.

In addition, the guard interval can be inserted into the OFDM symbolthrough a cyclic prefix scheme, in which predetermined final samples ofthe OFDM symbols in a time domain are copied and the copied samples areinserted into effective OFDM symbols, or through a cyclic postfixscheme, in which predetermined fore samples of the OFDM symbols in thetime domain are copied and the copied samples are inserted intoeffective OFDM symbols.

After receiving the signal from the guard interval inserter 227, thedigital to analog converter 229 converts the signal into an analogsignal and outputs the analog signal to the RF processor 231. The RFprocessor 231 includes a filter and a front end unit, and transmits theanalog signal through a transmission antenna, after RF-processing theanalog signal.

FIG. 3 is a schematic view illustrating an interleaving procedure forthe sub-channel signal in the IEEE 802.16e communication systemaccording to an embodiment of the present invention. However, prior toexplaining FIG. 3, it should be noted that the frequency reuse factor of1 is applied to the IEEE 802.16e communication system. In addition, eachof the sub-channels allocated from cells, that is, allocated from basestations(BSs) of the IEEE 802.16e communication system consists of aplurality of adjacent sub-carriers.

As described above, the sub-channel can be formed by dispersing 48sub-carriers over the frequency bands of the IEEE 802.16e communicationsystem, or by aligning the sub-carriers in the form of adjacentsub-carriers, such that 48 adjacent sub-carriers may form onesub-channel.

According to the present invention, the sub-channel is formed using theadjacent sub-carriers. In this case, as described above, the adjacentcells select the sub-channels having the same frequency band. If thesame MCS is applied to the selected sub-channels, the sub-channelsignals transmitted from one cell may act as interference signals withrespect to other cell. Therefore, a problem may occur when restoring thesignals that have been transmitted from each BS. That is, even if BSstransmit the signals with sufficient redundancy by taking interferenceof adjacent BSs into consideration, a subscriber station (SS)communicating with a corresponding BS may restore a signal having higherstrength between a signal transmitted from the corresponding BS and aninterference signal.

The sufficient redundancy signifies a predetermined condition forrestoring an original transmission signal when noise identical to theinterference is received together with the signal instead of theinterference signal to which the same MCS is applied.

The reason for decoding the signal having higher strength between thereceiving signal and the interference signal can be found from thecharacteristics of the decoder of the SS.

The decoder of each SS is a system capable of selecting a codewordsimilar to a receiving signal from among all codewords available in apredetermined coding system. Accordingly, if the same MCS is applied tothe same sub-channels, the decoder of each SS cannot detect the codewordtransmitted from the BS making communication with the SS. As a result,the decoder only detects the codeword included in the receiving signalhaving highest strength. Accordingly, the SS cannot communicate with thecorresponding BS.

In order to solve this problem, the decoder is designed such that itregards only codewords transmitted from the corresponding BS ascodewords generated from the coding system. Therefore, according to thepresent invention, the sub-channel has a function capable ofdistinguishing the BSs thereof. That is, although the sub-channel ofeach BS includes the same sub-carriers, it is possible to vary a mappingorder of the symbol to the sub-carriers to enable the sub-channel tohave the BS distinguishing function.

According to the present invention, the sub-channel signal istransmitted while mapping the sub-channel signal with the sub-channel,after interleaving the sub-channel signal to be transmitted, therebypreventing the sub-channel signal from operating as the interferencesignal to the adjacent cells.

FIG. 3 illustrates the interleaving scheme for the sub-channel signalused for a predetermined BS A and the interleaving scheme for thesub-channel signal used for the other BS B, which is adjacent to the BSA. It is assumed that the BSs A and B utilize N sub-carriers in which Madjacent sub-carriers form one sub-channel in a time-frequency domain.Herein, the N sub-carriers refer to a set of sub-carriers for K OFDMsymbols, where K is a predetermined positive integer.

Because the IEEE 802.16e communication system has a frequency reusefactor of 1 and forms the sub-channel by using the adjacentsub-carriers, positions of the sub-carriers forming the n^(th)sub-channel in the BSs A and B may be identical to each other. In thiscase, because the sub-carriers forming the n^(th) sub-channel in the BSsA and B have the same frequency band, the sub-channel signal isinterleaved. Accordingly, the mapping order of the sub-carrier for datasymbols forming the n^(th) sub-channel signal of the BSs A and B, thatis, the mapping order of the sub-carrier for modulation symbols, can beformed differently, depending on the modulation symbols.

For example, if the IEEE 802.16e communication system utilizes 1702sub-carriers, it is assumed that 166 sub-carriers are used as pilotsub-carriers, 1536 sub-carriers are used as data sub-carriers, and the1536 data sub-carriers are divided into 32 sub-channels including 48data sub-carriers, respectively. Accordingly, one sub-channel includes48 data sub-carriers.

Each sub-channel of the BSs A and B includes 48 data sub-carriers,including first to forty eighth data sub-carriers, in which the 48sub-carriers have the same frequency band. In addition, assuming thatthe signal mapped with each sub-carrier is the modulation symbol, thesub-channel signal including 48 modulation symbols is transmittedthrough one sub-channel. Accordingly, the interleaving pattern of thesub-channel signal for the BS A is set differently from the interleavingpattern of the sub-channel signal for the BS B, thereby preventing thesub-channel signal transmitted from the adjacent BS from operating asthe interference signal. Herein, the interleaving pattern for thesub-channel signal is referred to as a “sub-channel signal interleavingpattern”.

As illustrated in FIG. 3, according to the sub-channel signalinterleaving pattern of the BS A, 48 modulation symbols are sequentiallymapped with the sub-carriers of {2, 14, 1, . . . , 13, 3, 9}. Inaddition, according to the sub-channel signal interleaving pattern ofthe BS B, 48 modulation symbols are sequentially mapped with thesub-carriers of {7, 13, 5, . . . , 1, 8, 23}.

The sub-channel signal interleaving patterns must be set differentlyfrom each other depending on the BSs forming the IEEE 802.16ecommunication system. Accordingly, the following matters must beconsidered when setting the sub-channel signal interleaving patterns.

First, because one sub-channel includes M data sub-carriers, the mappingorder of the sub-carrier for the modulation symbols transmitted throughthe sub-channel, that is, the sub-channel signal interleaving pattern,is set using a sequence having a length M including elements {0, 1, . .. , M−1}. Each of the elements (0, 1, . . . , M−1) is used once in thesequence having the length M. The sub-channel signal interleavingpattern can be determined through various schemes as described below byusing the sequence having the length M.

(1) Random Search Scheme

(1-1) The Sub-Channel Signal Interleaving Pattern can be Determined byUsing an Orthogonal Sequence Having a Length M.

As described above, one sub-channel includes M data sub-carriers, suchthat it is possible to create orthogonal sequences having the length M.Herein, the orthogonal sequence signifies a sequence, in which the sameelements does not exist in the same location when selecting twosequences from among orthogonal sequences having the length M.

In addition, the orthogonal sequence having the length M can be createdthrough various schemes as described below.

First, orthogonal sequences having the length M, which are orthogonal toeach other, can be created by enabling the sequence of {0, 1, . . . ,M−1} to undergo a cyclic shift by [0, M−1] times.

Second, orthogonal sequences having the length M can be created througha computer simulation. Each of the orthogonal sequences having thelength M created through the above first and second schemes is allocatedas an interleaving pattern for each sub-channel signal of each BS,thereby preventing the signal of each BS from operating as theinterference signal of the adjacent BS.

(1-2) The Sub-Channel Signal Interleaving Pattern can be Determined byUsing a Non-Orthogonal Sequence Having a Length M.

If the number C of the BSs forming the IEEE 802.16e communication systemis larger than the length M of the sequence, the number of theorthogonal sequences is less than the number C of the BSs, therebymaking it impossible to distinguish all BSs by using the orthogonalsequence. Accordingly, a larger amount of non-orthogonal sequence iscreated by attenuating orthogonality of the orthogonal sequence, therebydistinguishing the BSs from each other. That is, there are provided M!sequences having the length M including elements {0, 1, . . . , M−1}, inwhich each of the elements {0, 1, . . . , M−1} is used once in thesequence.

In this case, when selecting two sequences from among M! sequences, itis possible to select the sequences corresponding to the number C of theBSs in which the sequences include a predetermined number ofsub-carriers having collision characteristics less than H sub-carriers.In particular, if the number of sequences including a predeterminednumber of sub-carriers having collision characteristics less than Hsub-carriers exceeds the number C of BSs, it is possible to select thesequence in such a manner that the BSs can be distinguished in anascending order based on the number of sub-carriers having the collisioncharacteristics.

The non-orthogonal sequences having the length M can be created throughthe computer simulation. Each of the non-orthogonal sequences having thelength M is allocated through the interleaving pattern of thesub-channel signal of each BS, thereby preventing the signal of each BSfrom operating as the interference signal of the adjacent BS.

(2) Cyclic Shift and Modulo Addition Scheme

Among orthogonal sequences having a length M including elements {0, 1, .. . , M−1}, in which each of the elements {0, 1, . . . , M−1} is usedonce in the sequence, a predetermined orthogonal sequence S₀ is definedas a basic orthogonal sequence. It is possible to create M² sequencesusing the basic orthogonal sequence S₀. Hereinafter, a method forcreating the M² sequences will be described.

First, it is assumed that a sequence S_(f) ^(g) has a predeterminedremainder after cyclic-shifting the basic orthogonal sequence S₀ f timesand dividing each element of the basic orthogonal sequence S₀ by M,while adding an offset g to the element, in which f and g have aninteger value existing within a range of [0,M−1]. That is, sequenceS_(f) ^(g) can be obtained through a modulo operation by using M.Accordingly, it is possible to create total M² sequences S_(f) ^(g). Thesequences, which undergo the cyclic shift by f times with the sameoffset g, have orthogonality to each other. The sequences havingparameters g and f of different values may enable collision betweenelements of the sequences.

The interleaving pattern of the sub-channel signal for each BS can bedetermined using the M² orthogonal sequences. In general, the maximumnumber C of BSs forming the IEEE 802.16e communication system is limitedto several hundreds. Therefore, it is possible to allocate thesub-channel signal interleaving pattern if the M has an integer valuemore than 20.

In addition, if the number C of the BSs is less than M², as describedabove, the sequences including a relatively smaller number ofsub-carriers having the collision characteristics can be selected forallocating the interleaving pattern of the sub-channel signal for the CBSs.

The sub-channel signal interleaving pattern can be determined accordingto the schemes for selecting the basic orthogonal sequence S₀.Hereinafter, the schemes for selecting the basic orthogonal sequence S₀will be described.

First, the basic orthogonal sequence S₀ is selected in such a mannerthat the number of sub-carriers having the collision characteristics canbe minimized in each of the M² sequences. That is, C sequences areselected corresponding to the number C of BSs in which the C sequencesinclude a predetermined number of sub-carriers, which may presentcollision characteristics when selecting two sequences from among the M²sequences, less than H sub-carriers. The selected C sequences are formedas a sequence sub-set. As described above, the C sequences that form thesequence sub-set can be selected through the computer simulation.

(3) Reed Solomon Sequence Scheme

When M=Q^(p)−1, wherein Q is a decimal and p is an integer, thesub-channel signal interleaving pattern can be determined using a ReedSolomon sequence defined in a Galois Field (GF, Q^(p)). If thesub-channel signal interleaving pattern is determined using the ReedSolomon sequence, the Reed Solomon sequence may include a maximum ofthree sub-carriers having the collision characteristics. Herein, j^(th)element of the Reed Solomon sequence is represented as P_(f) ^(g)(j),which satisfies Equation (1).

$\begin{matrix}{{P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.} & (1)\end{matrix}$

In Equation (1), P₀ represents a basic orthogonal sequence in the GF(Q^(p)), and P_(f)(j) represents a j^(th) element of a cyclic shiftorthogonal sequence, which is created through cyclic-shifting P₀ in theleft direction by f. In addition, P_(f) ^(g)(j) is a j^(th) element of asequence representing the sub-channel signal interleaving pattern. Theaddition operation in Equation (1) represents the addition operation inthe GF (Q^(p)). In addition, the total M(M+1) sequences used fordistinguishing the BSs are determined depending on the determinationschemes for parameters f and g.

According to the present invention, the parameters f and g aredetermined through one of following three schemes.

According to a first scheme, the parameter f has a predetermined integervalue selected from a predetermined integer range between 0 and M−1. Inaddition, the parameter g has a predetermined integer value selectedfrom a predetermined integer range between 0 and M.

The sub-channel signal interleaving pattern is allocated to the BSsthrough the following manner.

The sub-channel signal interleaving pattern is adapted for M orthogonalsequences and C to M sequences including a predetermined number ofsub-carriers having collision characteristics less than H sub-carriers.

First, predetermined serial numbers 0 to C−1 are allocated to the Csequences. That is, the sequences having a predetermined remainder afterdividing indexes of C BSs by C (C-modulo operation) are allocated to theC BSs. Herein, an index of a BS is an index assigned uniquely to the BSin the OFDMA communication system, so the OFDMA communication systemassigns indexes to a plurality of BSs of the OFDMA communication system.

Second, among C sequences, the number of sequences orthogonal to eachother is set smaller than the number of sequence representing thecollision characteristics, thereby allocating the sequences having thepredetermined remainder, after dividing the indexes of the BSs by C(C-modulo operation) to each BS.

Third, a system is designed in such a manner that the BSs having thesame remainder, after dividing the indexes of the BSs by C (C-modulooperation), are spaced from each other.

According to the second scheme, the parameters f and g are determinedusing Equation (2).

$\begin{matrix}{{f = {{c\_ id}\mspace{14mu} {mod}\mspace{14mu} {PERM}}}{g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}}} & (2)\end{matrix}$

In Equation (2), a parameter PERM represents M (PERM=M), and a parameterOFFSET represents M+1 (OFFSET=M+1). In addition, └x┘ represents amaximum integer value which is not larger than x, c_id represents aindex of the BS, and mod represents a modulo operation.

According to the third scheme, the parameters f and g are determined byEquation (3).

$\begin{matrix}{{f = {\left( \left\lfloor \frac{c\_ id}{OFFSET} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {PERM}}}{g = {{c\_ id}\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}}} & (3)\end{matrix}$

In Equation (3), parameters PERM and OFFSET have the values identical tothose defined in Equation (2).

According to the above three schemes, the sub-channel signalinterleaving pattern for each BS is determined by using M(M+1)orthogonal sequences which satisfy Equation 1.

If the number C of the BSs is less than M(M+1), as described above, theorthogonal sequences including a relatively smaller number ofsub-carriers having the collision characteristics are selected toallocate the sub-channel signal interleaving pattern for each of C BSs.

Hereinafter, a procedure of allocating the sub-channel signalinterleaving pattern when the number M of data sub-carriers forming onesub-channel is 48 (M=48).

As described above, a predetermined Reed Solomon sequence is selectedfrom among Reed Solomon sequences having the length M=48=Q²−1 (Q=7) as abasic orthogonal sequence P₀, thereby creating 48×49 sequences includinga maximum of three sub-carriers having the collision characteristics.Herein, the basic orthogonal sequence P₀ can be represented as shownbelow through septenary notation in Equation (4).

P₀={01,22,46,52,42,41,26,50,05,33,62,43,63,65,32,40,04,11,23,61,21,24,13,60,06,55,31,25,35,36,51,20,02,44,15,34,14,12,45,30,03,66,54,16,56,53,64,10}  (4)

In addition, the 48×49 sequences are allocated to each BS according tothe above three schemes.

FIG. 4 is a schematic view illustrating a procedure for transmitting thesub-channel signal in the IEEE 802.16e communication system according toan embodiment of the present invention. Referring to FIG. 4, wheninformation data to be transmitted is generated, as described withreference to FIG. 2, the transmitter creates a modulation symbol arrayby performing the CRC bit insertion, encoding, and symbol mappingprocesses with respect to the information data in step 411. Thetransmitter interleaves the modulation symbol array according to thesub-channel signal interleaving pattern, which has been preset in thetransmitter, in step 413. Because the schemes for determining thesub-channel signal interleaving pattern have already been describedabove, they will not again be described below.

In step 415, the transmitter allocates the interleaved sub-channelsignal to the corresponding sub-channel, that is, to the sub-carriersforming the corresponding sub-channel. In step 417, the transmittertransmits the sub-channel signal, thereby completing the procedure fortransmitting the sub-channel signal.

As described above with reference to FIG. 2, the sub-channel signaltransmission procedure includes the steps of converting the serialsignal allocated to the sub-channel to the parallel signal, insertingthe pilot symbol into the parallel signal, performing the IFFT withrespect to the parallel signal, converting the parallel signal into theserial signal, inserting the guard interval into the serial signal,converting the serial signal into the analog signal, and RF-processingthe analog signal.

Although the present invention has been described in relation to theschemes for determining the sub-channel signal interleaving pattern, thepresent invention is also applicable for changing the mapping positionof the sub-carriers because the process for interleaving of thesub-channel signal according to the interleaving pattern issubstantially identical to the process for changing the position of thesub-carriers forming the sub-channel. That is, according to the presentinvention, the sub-channel signal interleaving pattern can be replacedwith the mapping pattern of the sub-carriers forming the sub-channel.

As described above, according to the present invention, the sub-channelsignals allocated with the same frequency band to adjacent cells in theOFDMA communication system are transmitted by interleaving thesub-channel signals according to the sub-channel signal interleavingpattern, such that interference caused by the sub-channel signal of theadjacent cell can be minimized, thereby improving system performance.

While the present invention has been shown and described with referenceto certain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as defined by the appended claims.

1. A method for receiving symbols by a mobile subscriber station (MSS)in a communication system, the method comprising: receiving symbols froma base station (BS), wherein the symbols are mapped onto datasub-carriers using a sequence, wherein the sequence includes resultvalues, the result values being generated by applying, to a basicsequence, an offset and a number of cyclic shifting, the basic sequencehaving a length identical to the number of data sub-carriers, whereinthe sequence is expressed as: ${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$ where P_(f) ^(g)(j) is a j^(th) element of thesequence, P_(f)(j) is a j^(th) element of the cyclic shifted basicsequence, which is generated by cyclic-shifting the basic sequence in aleft direction by f times, f is an integer value selected from 0 to M−1,g is the offset having an integer value from 0 to M, and M is the numberof the data sub-carriers, and wherein f and g are determined accordingto: f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$wherein, PERM is M which is the number of data sub-carriers, OFFSET isM+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.
 2. The method as claimed inclaim 1, wherein, when M is 48, the basic sequence is formed in a Galoisfield and represents {01, 22, 46, 52, 42, 41, 26, 50, 05, 33, 62, 43,63, 65, 32, 40, 04, 11, 23, 61, 21, 24, 13, 60, 06, 55, 31, 25, 35, 36,51, 20, 02, 44, 15, 34, 14, 12, 45, 30, 03, 66, 54, 16, 56, 53, 64, 10}.3. A method for transmitting symbols by a mobile subscriber station(MSS) in a communication system, the method comprising: transmittingsymbols to a base station (BS), wherein the symbols are mapped onto datasub-carriers using a sequence, wherein the sequence includes resultvalues, the result values being generated by applying, to a basicsequence, an offset and a number of cyclic shifting, the basic sequencehaving a length identical to the number of data sub-carriers, whereinthe sequence is expressed as: ${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$ where P_(f) ^(g)(j) is a j^(th) element of thesequence, P_(f)(j) is a j^(th) element of the cyclic shifted basicsequence, which is generated by cyclic-shifting the basic sequence in aleft direction by f times, f is an integer value selected from 0 to M−1,g is the offset having an integer value from 0 to M, and M is the numberof the data sub-carriers, and wherein f and g are determined accordingto: f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$wherein, PERM is M which is the number of data sub-carriers, OFFSET isM+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.
 4. The method as claimed inclaim 3, wherein, when M is 48, the basic sequence is formed in a Galoisfield and represents {01, 22, 46, 52, 42, 41, 26, 50, 05, 33, 62, 43,63, 65, 32, 40, 04, 11, 23, 61, 21, 24, 13, 60, 06, 55, 31, 25, 35, 36,51, 20, 02, 44, 15, 34, 14, 12, 45, 30, 03, 66, 54, 16, 56, 53, 64, 10}.5. A method for transmitting symbols by a base station (BS) in acommunication system, the method comprising: transmitting symbols to amobile subscriber station (MSS), wherein the symbols are mapped ontodata sub-carriers using a sequence, wherein the sequence includes resultvalues, the result values being generated by applying, to a basicsequence, an offset and a number of cyclic shifting, the basic sequencehaving a length identical to the number of data sub-carriers, whereinthe sequence is expressed as: ${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$ where P_(f) ^(g)(j) is a j^(th) element of thesequence, P_(f)(j) is a j^(th) element of the cyclic shifted basicsequence, which is generated by cyclic-shifting the basic sequence in aleft direction by f times, f is an integer value selected from 0 to M−1,g is the offset having an integer value from 0 to M, and M is the numberof the data sub-carriers, and wherein f and g are determined accordingto: f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$wherein, PERM is M which is the number of data sub-carriers, OFFSET ism+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.
 6. The method as claimed inclaim 5, wherein, when M is 48, the basic sequence is formed in a Galoisfield and represents {01, 22, 46, 52, 42, 41, 26, 50, 05, 33, 62, 43,63, 65, 32, 40, 04, 11, 23, 61, 21, 24, 13, 60, 06, 55, 31, 25, 35, 36,51, 20, 02, 44, 15, 34, 14, 12, 45, 30, 03, 66, 54, 16, 56, 53, 64, 10}.7. A method for receiving symbols by a base station (BS) in acommunication system, the method comprising: receiving symbols from amobile subscriber station (MSS), wherein the symbols are mapped ontodata sub-carriers using a sequence, wherein the sequence includes resultvalues, the result values being generated by applying, to a basicsequence, an offset and a number of cyclic shifting, the basic sequencehaving a length identical to the number of data sub-carriers, whereinthe sequence is expressed as: ${P_{f}^{g}(j)} = \left\{ \begin{matrix}{{P_{f}(j)} + g} & {{{P_{f}(j)} + g} \neq 0} \\g & {{{P_{f}(j)} + g} = 0}\end{matrix} \right.$ where P_(f) ^(g)(j) is a j^(th) element of thesequence, P_(f)(j) is a j^(th) element of the cyclic shifted basicsequence, which is generated by cyclic-shifting the basic sequence in aleft direction by f times, f is an integer value selected from 0 to M−1,g is the offset having an integer value from 0 to M, and M is the numberof the data sub-carriers, and wherein f and g are determined accordingto: f = c_id  mod  PERM$g = {\left( \left\lfloor \frac{c\_ id}{PERM} \right\rfloor \right)\mspace{14mu} {mod}\mspace{14mu} {OFFSET}}$wherein, PERM is M which is the number of data sub-carriers, OFFSET isM+1, └x┘ represents a maximum integer value, which is not greater thanx, and c_id represents a predefined value.
 8. The method as claimed inclaim 7, wherein, when M is 48, the basic sequence is formed in a Galoisfield and represents {01, 22, 46, 52, 42, 41, 26, 50, 05, 33, 62, 43,63, 65, 32, 40, 04, 11, 23, 61, 21, 24, 13, 60, 06, 55, 31, 25, 35, 36,51, 20, 02, 44, 15, 34, 14, 12, 45, 30, 03, 66, 54, 16, 56, 53, 64, 10}.